Regular Expression Question

[Ron Rohrssen]

Slightly off topic....

How can I write a regex that limits user input to 3 digits in the range of
1-128?

I've been trying \d{1,128} but this allows for a match on more than 3
digits.

Thanks.

[Eric Gunnerson [MS]]

Ron,

A couple of thoughts.

This is the sort of expression that lends itself quite well to brute-force
testing. It's pretty easy for you to throw a whole mess of values at it
(even the whole Int32 range) to see how it behaves.

My general approach is not to do this kind of thing in regex, as it's so
tough to read and debug. It's much easier to do it in code.

If you do, here's my advice:

1) Download my regex tool from here:

http://www.gotdotnet.com/Community/U...1-4EE2729D7322

2) Write your regexes like:

string pattern = @"
(
\d | # any single digit number
\d\d | # any two-digit number
1[01]\d # 10d or 11d
12[0-8] # 120 - 128
)
"

You'll need to use RegexOptions.Ig norePatternWhit espace

--
Eric Gunnerson

Visit the C# product team at http://www.csharp.net
Eric's blog is at http://weblogs.asp.net/ericgu/

This posting is provided "AS IS" with no warranties, and confers no rights.
"Ron Rohrssen" <rl******@fight spam.rockwellco llins.com> wrote in message
news:eY******** *****@TK2MSFTNG P11.phx.gbl...

Agreed!

I use regular expressions about once every 2 years. I still haven't found a straight forward tutorial that doesn't take days to read through. I even
bought the O'Reilly Regular Expressions book when I was doing some Perl
several years ago. At the time I found it pretty useful. But like most
things, if you don't use it, you lose it.

Do you have any "favorite" sites or books that you like to use for
reference?

Ron
"Jon Skeet [C# MVP]" <sk***@pobox.co m> wrote in message
news:MP******** *************** *@msnews.micros oft.com...

Ron Rohrssen <rl******@fight spam.rockwellco llins.com> wrote:

Yes, I see the overlap now. Thanks.

> \b(12[0-8] | 1[0-1][0-9] | 0?[0-9]?[0-9])\b

What does the ? mean in your regex?

It's basically "the preceding character is optional".

I really wouldn't start messing around with regular expressions like
this without reading a thorough tutorial on it and having MSDN handy,
personally.

--
Jon Skeet - <sk***@pobox.co m>
http://www.pobox.com/~skeet
If replying to the group, please do not mail me too

[Daniel Billingsley]

I also found a tool called "The Regex Coach" which was invaluable. It has a
feature to "step" through the evaluation so you can see exactly when things
match or go haywire. It's a standard regex tool and doesn't support all the
features of the .NET implementation.

"Eric Gunnerson [MS]" <er****@online. microsoft.com> wrote in message
news:OJ******** ******@TK2MSFTN GP12.phx.gbl...

Ron,

A couple of thoughts.

This is the sort of expression that lends itself quite well to brute-force
testing. It's pretty easy for you to throw a whole mess of values at it
(even the whole Int32 range) to see how it behaves.

My general approach is not to do this kind of thing in regex, as it's so
tough to read and debug. It's much easier to do it in code.

If you do, here's my advice:

1) Download my regex tool from here:

http://www.gotdotnet.com/Community/U...1-4EE2729D7322
2) Write your regexes like:

string pattern = @"
(
\d | # any single digit number
\d\d | # any two-digit number
1[01]\d # 10d or 11d
12[0-8] # 120 - 128
)
"

You'll need to use RegexOptions.Ig norePatternWhit espace

--
Eric Gunnerson

Visit the C# product team at http://www.csharp.net
Eric's blog is at http://weblogs.asp.net/ericgu/

This posting is provided "AS IS" with no warranties, and confers no rights. "Ron Rohrssen" <rl******@fight spam.rockwellco llins.com> wrote in message
news:eY******** *****@TK2MSFTNG P11.phx.gbl...

Agreed!

I use regular expressions about once every 2 years. I still haven't

found a

straight forward tutorial that doesn't take days to read through. I even
bought the O'Reilly Regular Expressions book when I was doing some Perl
several years ago. At the time I found it pretty useful. But like most
things, if you don't use it, you lose it.

Do you have any "favorite" sites or books that you like to use for
reference?

Ron
"Jon Skeet [C# MVP]" <sk***@pobox.co m> wrote in message
news:MP******** *************** *@msnews.micros oft.com...

Ron Rohrssen <rl******@fight spam.rockwellco llins.com> wrote:
> Yes, I see the overlap now. Thanks.
>
> > \b(12[0-8] | 1[0-1][0-9] | 0?[0-9]?[0-9])\b
>
> What does the ? mean in your regex?

It's basically "the preceding character is optional".

I really wouldn't start messing around with regular expressions like
this without reading a thorough tutorial on it and having MSDN handy,
personally.

--
Jon Skeet - <sk***@pobox.co m>
http://www.pobox.com/~skeet
If replying to the group, please do not mail me too